fix: make sure last slice is included in iterate slices (#398)

doc/release_notes.rst

@@ -4,6 +4,8 @@ Release Notes
 Upcoming Version
 ----------------
 
+
+* IMPORTANT BUGFIX: The last slice of constraints was not correctly written to LP files in case the constraint size was not a multiple of the slice size. This is fixed now.
 * Solution files that following a different naming scheme of variables and constraints using more than on initial letter in the prefix (e.g. `col123`, `row456`) are now supported.
 
 Version 0.4.3

linopy/common.py

@@ -519,7 +519,7 @@ def iterate_slices(
         return
 
     # number of slices
-    n_slices = max(size // slice_size, 1)
+    n_slices = max((size + slice_size - 1) // slice_size, 1)
 
     # leading dimension (the dimension with the largest size)
     sizes = {dim: ds.sizes[dim] for dim in slice_dims}
@@ -533,12 +533,12 @@ def iterate_slices(
     if size_of_leading_dim < n_slices:
         n_slices = size_of_leading_dim
 
-    chunk_size = ds.sizes[leading_dim] // n_slices
+    chunk_size = (ds.sizes[leading_dim] + n_slices - 1) // n_slices
 
     # Iterate over the Cartesian product of slice indices
     for i in range(n_slices):
         start = i * chunk_size
-        end = start + chunk_size
+        end = min(start + chunk_size, size_of_leading_dim)
         slice_dict = {leading_dim: slice(start, end)}
         yield ds.isel(slice_dict)
 

test/test_common.py

@@ -522,6 +522,20 @@ def test_iterate_slices_slice_size_none():
         assert ds.equals(s)
 
 
+def test_iterate_slices_includes_last_slice():
+    ds = xr.Dataset(
+        {"var": (("x"), np.random.rand(10))},  # noqa: NPY002
+        coords={"x": np.arange(10)},
+    )
+    slices = list(iterate_slices(ds, slice_size=3, slice_dims=["x"]))
+    assert len(slices) == 4  # 10 slices for dimension 'x' with size 10
+    total_elements = sum(s.sizes["x"] for s in slices)
+    assert total_elements == ds.sizes["x"]  # Ensure all elements are included
+    for s in slices:
+        assert isinstance(s, xr.Dataset)
+        assert set(s.dims) == set(ds.dims)
+
+
 def test_iterate_slices_empty_slice_dims():
     ds = xr.Dataset(
         {"var": (("x", "y"), np.random.rand(10, 10))},  # noqa: NPY002
@@ -542,6 +556,22 @@ def test_iterate_slices_invalid_slice_dims():
         list(iterate_slices(ds, slice_size=50, slice_dims=["z"]))
 
 
+def test_iterate_slices_empty_dataset():
+    ds = xr.Dataset(
+        {"var": (("x", "y"), np.array([]).reshape(0, 0))}, coords={"x": [], "y": []}
+    )
+    slices = list(iterate_slices(ds, slice_size=10, slice_dims=["x"]))
+    assert len(slices) == 1
+    assert ds.equals(slices[0])
+
+
+def test_iterate_slices_single_element():
+    ds = xr.Dataset({"var": (("x", "y"), np.array([[1]]))}, coords={"x": [0], "y": [0]})
+    slices = list(iterate_slices(ds, slice_size=1, slice_dims=["x"]))
+    assert len(slices) == 1
+    assert ds.equals(slices[0])
+
+
 def test_get_dims_with_index_levels():
     # Create test data